A. Field of the Invention
This invention relates to the field of oil well stimulation, drilling and recovery.
In particular, the invention relates to biocides for oil field water treatment and as preservatives for polymers used in oil field fluids and, especially, to preservatives in solid form which inhibit the growth of bacteria in oil field waters and on polymers used in oil field well stimulation and drilling fluids.
Polymers are used in the oil industry in methods of well stimulation, drilling and recovery. In the use of polymers, for example, in water flood, fracturing and drilling fluids, the polymers are subjected to an environment conducive to bacterial growth. The growth of the bacteria on polymers used in such fluids can materially alter the physical characteristics of the fluids. For example, bacterial action can deteriorate the polymer, leading to loss of viscosity and subsequent ineffectiveness of the fluids. Fluids which are especially susceptible to bacterial degradation are those which contain polysaccharide and synthetic polymers. The term "oil field fluids" as used herein is meant to include those fluids having oil field applications and whose viscosity has been increased with polymers, whether polysaccharide and/or synthetic. The term "oil field waters" as used herein includes waters used in secondary recovery, and water used to hydrate the polymers and water used in tertiary or EOR (enhanced oil recovery) methods.
Although biocides have been used in the past to treat oil field waters and oil field fluids used in oil field operations, they have been used, predominantly, in liquid form and, due to their very nature, must be handled with caution to avoid eye and skin contact from splashing. Also, the use of liquid biocides risks contamination of potable water sources from spilled biocides. Accordingly, there is a need for a safer form of biocides to avoid personal and environmental contamination.
B. Prior Art
U.S. Pat. No. 3,699,231 discloses the use of an aldehyde/carbamate mixture to inhibit bacterial action. U.S. Pat. No. 3,929,561 discloses a biocide mixture of 5-chloro-2-methyl-4-isothiazole-e-one, 2-methyl-4-isothiazolin-e-one and a sulfone.
U.S. Pat. Nos. 4,129,448 and 4,165,318 disclose mildew stabilization of acrylic emulsion polymr paints by using 3-isothiazolones as mildewcides and formaldehyde to stabilize the isothiazolones.
U.S. Pat. No. 4,295,932 discloses a microbial inhibiting mixture of 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one and chlorine or chlorine dioxide.